Removing CO2 and, if necessary, H2 S from gases

Abstract

CO 2 and, if necessary, H 2 S are removed from a gas which contains CO 2 and may contain H 2 S with an absorption liquid by a process in which the gas which contains CO 2 and may contain H 2 S is treated in an absorption zone with the absorption liquid, the treated gas is removed from the absorption zone, the absorption liquid which is obtained from the absorption zone and is laden with CO 2 and may be laden with H 2 S is then regenerated in that the said absorption liquid is let down in one or more let-down stages and a let-down gas is taken off at the top of the first let-down stage or, in the case of a plurality of let-down stages, at the top of one or more of the first to penultimate let-down stages, and the partially regenerated absorption liquid obtained from the last let-down stage is, if required, fed to a stripping zone for further regeneration, one or more acid gas streams which contain the CO 2 and may contain H 2 S being removed from the regeneration stage and the regenerated absorption liquid being recycled to the absorption zone, wherein a bleed stream of completely or partially regenerated absorption liquid is fed to one or more of the let-down stages from which the let-down gas is removed, at a point above the feed of the absorption liquid to be let down.

We claim: 
     
       1. A process for removing CO 2  and, if present, H 2  S, from a gas containing CO 2  by contact with an absorption liquid which comprises: treating the gas containing CO 2  with the absorption liquid in an absorption zone; regenerating the absorption liquid which is obtained from the absorption zone and which is laden with CO 2  by reducing the pressure of the CO 2  -laden liquid in two to four let-down stages; taking off a gas containing CO 2  at the top of one or more of the let-down stages; recycling the regenerated absorption liquid from one or more of the said let-down stages to the absorption zone and feeding a bleed stream of said regenerated absorption liquid to one or more of the let-down stages from which a gas containing CO 2  is taken off, the gas being taken off at a point above the feed of the absorption liquid therein. 
     
     
       2. A process as defined in claim 1, wherein the regenerated liquid from the let-down stage is fed to a stripping zone for further regeneration. 
     
     
       3. A process as defined in claim 1, wherein the gas which contains CO 2  and may contain H 2  S is first treated with absorption liquid in a first absorption stage, the gas obtained at the top of the first absorption stage is fed to a second absorption stage, in which, for further removal of CO 2  and, where relevant, H 2  S, it is treated with absorption liquid which has a lower content of CO 2  and, where relevant, H 2  S than the absorption liquid fed to the first absorption stage, the treated gas is taken off at the top of the second absorption stage, the aqueous absorption liquid initially laden with CO 2  and, where relevant, H 2  S and obtained at the bottom of the second absorption stage is fed to the top of the first absorption stage, the absorption liquid which is laden with CO 2  and may be laden with H 2  S and is obtained in the lower part of the first absorption stage is regenerated by being reduced in pressure in two to four let-down stages, a bleed stream of the stream of absorption liquid obtained at the bottom of the last let-down stage is recycled to the first absorption stage, a further bleed stream of the stream of absorption liquid obtained at the bottom of the last let-down stage is fed to one or more of the first to penultimate let-down stages, a further stream of absorption liquid obtained at the bottom of the last let-down stage is fed to a stripping zone for further regeneration, and the regenerated absorption liquid obtained at the bottom of the stripping zone is recycled to the second absorption stage. 
     
     
       4. A process as defined in claim 1, wherein the gas which contains CO 2  and may contain H 2  S is treated with absorption liquid in an absorption stage, the treated gas is taken off at the top of the absorption stage, the absorption liquid which is laden with CO 2  and may be laden with H 2  S and is obtained in the lower part of the absorption stage is regenerated by being reduced in pressure in two or more let-down stages and is fed to a stripping zone for further regeneration, a bleed stream of the stream of absorption liquid obtained at the bottom of the last let-down stage and a bleed stream of the stream of absorption liquid obtained at the bottom of the stripping zone are fed to one or more of the first to penultimate let-down stages, and the stream of absorption liquid obtained at the bottom of the stripping zone is completely or partially recycled to the absorption stage. 
     
     
       5. A process as defined in claim 1, wherein the gas which contains CO 2  and may contain H 2  S is treated with absorption liquid in an absorption stage, the treated gas is taken off at the top of the absorption stage, the absorption liquid which is laden with CO 2  and may be laden with H 2  S and is obtained in the lower part of the absorption stage is regenerated by being reduced in pressure in two to four let-down stages, a bleed stream of the stream of absorption liquid obtained at the bottom of the last let-down stage is fed to one or more of the first to penultimate let-down stages, and a further bleed stream of the stream of absorption liquid obtained at the bottom of the last let-down stage is recycled to the absorption stage. 
     
     
       6. A process as defined in claim 1, wherein the absorption liquid used is a physical solvent. 
     
     
       7. A process as claimed in claim 6, wherein the absorption liquid used is a polyethylene glycol dialkyl ether. 
     
     
       8. A process as defined in claim 1, wherein the absorption liquid used is a chemical solvent. 
     
     
       9. A process as claimed in claim 8, wherein the absorption liquid used is an aqueous solution containing from 20 to 70% by weight of methyldiethanolamine. 
     
     
       10. A process as defined in claim 1, wherein one or more of the gases from the let-down stages are recycled to the absorption zone.